JOEL SAGET/AFP/Getty Images(NEW YORK) -- As the U.S. military began pulling back on the ground in Afghanistan in 2012, it greatly upped the number of drone strikes.

The United Nations reported on Tuesday that more than 500 weapons were fired from unmanned drones last year, compared to fewer than 300 in 2011.

Unlike Pakistan where leaders have said that drone attacks on suspected Taliban and al Qaeda terrorists violate its national sovereignty, Afghan President Hamid Karzai has been largely silent on the issue.

For the most part, the drone strikes are intended to back up American ground forces as they conduct operations in Afghanistan. Meanwhile, the use of drones has enabled U.S. soldiers to step back from their front-line roles and allow Afghan national forces to assume more security responsibilities.